1. Field of the Invention
The present invention relates to float switches.
2. Description of the Prior Art
A wide variety of float switches are known to the prior art. Practically every toilet has a mechanical float switch. The present invention relates to electrical float switches which generate one or more selected electric signals as a function of liquid level. Typical examples include float switches in boats which activate pumps when the fluid level in the hull reaches a selected triggering level such as the type that applicant received a patent U.S. Pat. No. 3,621,168 on about 15 years ago.
Float switches are usually used in or near a water environment. Since water frequently has an adverse effect on electrical switches, great pain has been taken to isolate the electronics from the water environment. Unfortunately, such switches must work for a period of years in a water related environment, and the great length of time permits the water in a certain small percentage of cases, probably less than one percent, to cause the water to adversely effect switch operation. While 99+ percent sounds pretty good for reliability, this is small consolation to you if you happen to be an unlucky guy whose boat sank because the pump did not come on because the float switch finally gave out after three years or ten years or some other length of time. There has been no way up to the present of designing a float switch which could be easily checked to determine if it was going to give out in the near future.
Most of the switch failures could be predicted if one could predict that water was going to get into the switch cavity, come in contact with the switch sometime in the near future or if one could predict that it had already happened. Modern switches can withstand a certain amount of moisture in their vacinity, but if water gets into the switching environment the chance of failure is greatly multiplied.
The present invention comprises a visually testable float switch including testing means which remain in an expanded configuration when there is no leak between the external fluid environment and a switching cavity, which testing means switch to on unexpanded configuration when there is a leak between the fluid environment and the switching cavity. A simple glance at the switch permits the viewer to detect if there has been any change in the testing means which in turn acts as a good predicter of most switch failures. Various types of electric pickups can electronically monitor whether the expansion of the visual testing means is still present thereby indicating that no leak has occurred. The present system is particularly useful in quality control after manufacture of float switches, since the float switches need only be left alone for a little while and if defects as small as porosity defects permit leakage between the switch cavity and the external environment, they can be detected. Since air is so much more permeable than liquid, the retaining of air for a substantial period of time is a good indication of the fluid tight integrity of the switch, thereby alleviating prior art float switch quality control problems such as the near impossibility to predict which float switch will fail to work ten years in the future.
It is believed that the present invention is the first inexpensive system to really safeguard that difficult transition point where the float coupling means enters the switch container since the float coupling means must move as a function of liquid level, thereby making sealing more difficult.
Obviously, the same general technique used for a switch can be used to detect a leak into any submersible container, so the present invention has wider application than just merely float switches.